Creating new tabs in properties panel
SpaceProperties.context
This is the enum property that used to go across the top of properties area, rendered as tabs.

class bpy.types.SpaceProperties(Space)
Properties space data
context
        TOOL Tool, Active Tool and Workspace settings.
        SCENE Scene, Scene.
        RENDER Render, Render.
        OUTPUT Output, Output.
        VIEW_LAYER View Layer, View Layer.
        WORLD World, World.
        OBJECT Object, Object.
        CONSTRAINT Constraints, Object Constraints.
        MODIFIER Modifiers, Modifiers.
        DATA Data, Object Data.
        BONE Bone, Bone.
        BONE_CONSTRAINT Bone Constraints, Bone Constraints.
        MATERIAL Material, Material.
        TEXTURE Texture, Texture.
        PARTICLES Particles, Particles.
        PHYSICS Physics, Physics.
        SHADERFX Effects, Object visual effects.


In the python console
&gt;&gt;&gt; for a in C.screen.areas:
...     if a.type == 'PROPERTIES':
...         break
...         
&gt;&gt;&gt; s = a.spaces.active
&gt;&gt;&gt; s.context
'DATA'

&gt;&gt;&gt; s.rna_type.properties['context'].enum_items_static.keys()
['TOOL', 'SCENE', 'RENDER',
    'OUTPUT', 'VIEW_LAYER', 'WORLD', 
    'OBJECT', 'CONSTRAINT', 'MODIFIER', 
    'DATA', 'BONE', 'BONE_CONSTRAINT', 
    'MATERIAL', 'TEXTURE', 'PARTICLES',
    'PHYSICS', 'SHADERFX']

Setting the panels bl_context class property to a value above defines which &quot;tab&quot; it is in.
Trying to set an enum to an undefined value will throw an error, as opposed to setting bl_category in a 'TOOLS' panel which creates a new tab.
To make a new tab would need to somehow add an item whilst un-re-registering the property.  Perhaps this is doable, in the back of my mind there has been a question either here or on the blender artists forum.
The property is inter-twined with context.  I wouldn't mess with it.
Alternatives

choosing one of the above for your Panel context. Remember there is the ability to subpanel in 2.8 by defining a panels parent panel.
appending or prepending draw methods to existing panels. Prepending to a panel that is always at or near the top gives high vis easy access. IMO this is under-utilized.
&quot;take out&quot; (unregister) panel classes that you wish to replacce.  Eg overtake one of the conexts by unregistering other panels when in &quot;armory&quot; mode.
or redraw an existing panel.  Panels have a _drawfuncs list that can be manipulated at runtime.